Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.

"Beyond the myth lies America's greatest betrayal."

Spoiler Alert! Robert Ford Kills Jesse James.

Robert Ford is standing next to Jesse James in his yard somewhere in Missouri. James pulls two bullsnakes out of a container. Ford flinches when he sees them.
James asks: "You scared?"
Ford replies: "No just surprised a little."
James: "They ain't as succulent as I like and they're the devil to clean but if a man skins 'em fries 'em in garlic and oil, mercy them's good eatin'.
Ford: "Well, I never been that hungry."
James: "I give them names."
Ford: "Such as?"
James :"Such as enemies. I give them names of ememies."
Then he chops off both their heads with a pocket knife.
We see him later throw the bodies in the yard, so they were probably not killed for food, despite his cooking tips..

After looking at it several times, I'm convinced that the decapitation is real. You can see one of the tongues flick out part way a couple times just before the knife cuts the heads off. I was hoping that they had substituted two fake heads or dead snake heads during one of the two quick cuts away from the snakes, but the flicking tongue gives it away. I don't believe they would bother to fake the tongue. And that explains why there was no disclaimer that no animals were harmed during the making of this movie. I hope I'm wrong. There is no need to kill live animals for entertainment.

In the film the snakes are live Gopher Snakes, possibly Bull Snakes since most of the film was shot in Canada in the range of the Bull Snake.
In the book the snakes are "garden snakes" and Jesse says: "Must have at least twelve of these critters in the yard. Sometimes of an evening I'll sneak out here barefoot and listen to them slither over to where they don't think I can catch them. Then I snag them with my toes just to prove there's no getting away from Jesse."